There ave hitherto been known peristaltic finger pumps as a transfusion apparatus useful for an automatic dropper (for example, Japanese Laid-open Patent Application No. 58-165868). In such finger pumps, a flexible transfusion tube is squeezed by movement of a plurality of finger elements in the liquid-feeding direction for supplying a constant amount of a liquid.
It has been found from determination of a flow rate on the delivery side of the pump that an approximately trapezoidal wave form of delivery and an approximately V-shaped wave form of back flow upon release of a pressing action byt he finger element on the tranfusion tube are repeated (see FIG. 5). Thus, the conventional finger pumps can not maintain a constant flow rate on the delivery side and therefore may not be readily utilized for the automatic dropper.
From this viewpoint, there have been various proposals for maintaining the constant flow rate on the delivery side in the peristaltic pumps for suc an application. For example, Japanese Utility Model Publication No. 57-27463 discloses a transfusion apparatus for preventing the back flow, in which a time point of releasing a complete occlusion of the transfusion tube through rotation of a pressing element of the peristaltic pump is detected to provide a signal which allows a driving motor of the pump to rotate for a predetermined period of time at a higher velocity than its normal rotation, thereby to supplement a back flow portion in a short time. However, if the proposed transfusion apparatus is applied in the peristaltic finger pump, the driving motor of the finger pump is rotated faster than the normal rotation from a time point of releasing the complete occlusion of the tube (point P), as shown in FIG. 5. It is true that the period of back flow is reduced, but the delivery flow rate is still somewhat stagnated and the stagnation may not be neglected especially at the lower driving velocity of the pump, resulting in difficulty of its application in the automatically dropping transfusion apparatus.
Accordingly, the automatic dropping transfusion apparatus requires a flow rate characteristic of the pump having a stable flow rate and an accurate infusion over the wide flow range for its use of injecting a pharmaceutical liquid into a human body. In particular, the stable flow rate in the lower flow range is highly desired for infants and serious patients. For example, the peristaltic finger pump shows an approximately trapezoidal wave form of delivery and an approximately V-shaped wave form of the back flow upon release of the pressing and occluding action of the finger elements on the transfusion tube, so that the flow rate characteristic cannot be constant. For this reason, the pump of such type requires a drive control capable of approaching not only the increasing and decreasing ranges of the flow rate in the trapezoidal wave form but also the back flow wave form toward a predetermined flow rate.
In accordance with the invention, as shown in FIG. 5, for the flow rate characteristic of delivery from the transfusion tube accompanied with a certain peristaltic movement of the finger elements in the conventional peristaltic finger pump, the maximum delivery amount (DV.sub.M) of the trapezoidal wave form is set to a reference amount, and the instantaneous delivery amount (DVn) is determined at a given position (n). The peristaltic rate at this position is then set to be mutliplied by a factor of DV.sub.M /DVn in order to maintain the delivery amount at a constant value of DV.sub.m thereby to achieve the stable flow rate characteristic on the delivery side. The factor of DV.sub.M /DVn may be determined by previous experiments.